(Maybe?) Universal Snipe-IT pagination

[uberbrady]

So when we fetch Models, it looks like we fetch one page, and then, if needed, a second page. But that's it. (This may be the cause of #111). The function get_snipe_users seems to do things the right way, but isn't really user-specific - just about any method could do something similar. I suspect we can extract out the "iterate through offsets and page sizes until you get everything" logic into its own functions and just use it in both get_snipe_users as well as get_snipe_models.

It sounds like, according to @jerm, we might want to just steal most of this: grokability/kandji2snipe#13 - and that may handle most of the problem with #111 , anyways.

We don't want to fall into a situation where we're making 'perfect' the enemy of 'good'. And maybe that's just good enough.